There are several variants of the medical pendant out there, but most of them are rented against a contract and they get epensive over time..
You can get an app for a cell phone, which provides wider area coverage than the traditional 'plugged into the home phone line' systems.
And in the 'at home' systems you can choose from a monitored solution like the one from Philips, or, as an option you can elect a self-monitored solution where the device will call through a series of preprogrammed numbers, the last of which would be 911.
One nice feature of this latter solution is that the pendant is also a cordless cellphone and it supports multiple devices, like pendants for each of your parents, and fixed stations, which can be put in places like the bathroom.
As a cellphone the pendant can be used to answer incoming calls and you don't need to be in acoustic range of the base station as you do with the Philips system. And you just buy the system once. It's what I got for my father in his later years (I still have it sitting in it's box).
Here's a link: https://www.logicmark.com/products/unmonitored/freedom-alert/